Ion assisted deposition is a process for the creation of thin films in which a substrate is simultaneously, or nearly simultaneously, bombarded by a flux of evaporant material that forms the thin film and a flux of ions that enhances the thin film properties. The role of the ions can be to provide an additional source of energy, eg for densifying the growing film and for modifying the physical properties of the film such as the optical properties, hardness and the like. Alternatively or in addition, the ions may be used to modify the chemical properties of the film by reacting with the film, such as in the conversion of metal films to oxides or nitrides.
In all of these processes, it is important to know the rate of arrival of ions at the substrate in relation to the rate of arrival of evaporant material, known as the ion to atom arrival ratio. Here, the term atom is used loosely as it also covers the situation where molecules of evaporant are being deposited.
A problem that exists in the thin film industry is that it is difficult to measure the ion current during deposition because the detector has to be placed not only in the path of the ions, but also the evaporant. Because the evaporant is most commonly a dielectric material or a metal that is converted to a dielectric by ion bombardment, an insulating layer is formed on the detector that prevents further ions from being properly detected.
It is therefore an object of the present invention to provide a detector that can accurately measure a charged particle flux during a thin film deposition process.